Studies are continuing on the structure and biological activity of a salt-soluble chromatin obtained from rabbit thymus nuclear lysates via and endogenous nuclease reaction. A modified system using buffer-washed chromatin and the inclusion of the proteolytic inhibitor leupeptin has been developed. The conformation of the linker DNA in the chromatin complex and the question of its interaction with histone H1 will be investigated by a study of the changes in the circular dichroic (CD) spectra of H1-depleted ad H1-supplemented chromatin. Chromatin will be fractionated by sampling the endogenous reaction at different times. The various fractions will be characterized by gel electrophoresis and CD spectrum. H1-depleted chromatin will also be studied. The binding and initiation of rabbit thymus RNA polymerase II with these chromatin complexes will be correlated with protein profiles and chromatin conformation.